title: The effect of multiple N-methylation on intestinal permeability of cyclic hexapeptides.
abstract: Recent progress in peptide synthesis simplified the synthesis of multiple N-methylation of peptides. To evaluate how multiple N-methylation affects the bioavailability of peptides, a poly alanine cyclic hexapeptide library (n = 54), varying in the number of N-methyl (N-Me) groups (1-5 groups) and their position, was synthesized. The peptides were evaluated for their intestinal permeability in vitro using the Caco-2 model. Further evaluation of the transport route of chosen analogues was performed using rat excised viable intestinal tissue, a novel colorimetric liposomal model and the parallel artificial membrane permeability assay (PAMPA). While most members were found to have poor permeability (permeability coefficient, P(app) < 1 x 10⁻⁶ cm/s, lower than mannitol, the marker for paracellular permeability), 10 analogues were found to have high Caco-2 permeability, (P(app) > 1 x 10⁻⁵ cm/s, similar to testosterone, a marker of transcellular permeability). No correlation was found between the number of N-methylated groups and the enhanced permeability. However, 9/10 permeable peptides in the Caco-2 model included an N-Me placed adjacently to the D-Ala position. While the exact transport route was not fully characterized, the data suggests a facilitated diffusion. It can be concluded that multiple N-methylation of peptides may improve intestinal permeability, and therefore can be utilized in the design of orally available peptide-based therapeutics.
authors.affiliation: The Institute of Drug Research, School of Pharmacy, The Hebrew University of Jerusalem, Jerusalem 91120, Israel.
authors.forename: Oded
authors.initials: O
authors.lastname: Ovadia
authors.forename: Sarit
authors.initials: S
authors.lastname: Greenberg
authors.forename: Jayanta
authors.initials: J
authors.lastname: Chatterjee
authors.forename: Burkhardt
authors.initials: B
authors.lastname: Laufer
authors.forename: Florian
authors.initials: F
authors.lastname: Opperer
authors.forename: Horst
authors.initials: H
authors.lastname: Kessler
authors.forename: Chaim
authors.initials: C
authors.lastname: Gilon
authors.forename: Amnon
authors.initials: A
authors.lastname: Hoffman
mesh_terms: D000818:Animals; D001692:Biological Transport; D018938:Caco-2 Cells; D002463:Cell Membrane Permeability / Q000187:drug effects*; D003500:Cyclization; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects*; D007422:Intestines / Q000187:drug effects*; D008745:Methylation; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D051381:Rats
chemical_list: D009842:Oligopeptides; D010456:Peptides, Cyclic